The upside to "heavy for capacity" is that they have less recoil for caliber, and are more controllable in one handed shooting.
Weaver, Chapman, and isosceles holds help a lot with lighter, snappier guns. Being a firm believer in Murphy, though, I do not count on having both hands free, or even operable, during a self-defense situation.
Plus, with good gear (typically a Sam Andrews belt and MacDaniel IWB combo), I really do not notice the carry weight. And, single stack spare mags are easier to carry and conceal.